Plastic valves for liquid containers are known and used, for example, in the chemical, petrochemical, pharmaceutical, food industries and the like.
Certain liquids contained in containers can be highly corrosive, whereas others can have a milder corrosive effect. In use, the inner parts of valves are exposed to contact with the product in the container, even for long periods of time. As used herein, the term “inner parts” of a valve is meant to indicate the inner walls of the conduit for passage of the product, the closing member which shuts off product passage to prevent outflow, and the gasket thereof.
In addition to chemical aggressions, the liquid contained in containers also applies physical pressure to the inner parts of the valve, e.g. caused by the product weight or mechanical expansion or contraction stresses due to temperature changes or reactions within the product. This action is particularly problematic for the closing member which is the only movable part and is more exposed to such stresses, due to its construction. Therefore, a valve closing member shall ensure optimal performances both in terms of mechanical properties and chemical resistance with time.
Hence, it would be desirable to have valves that can provide optimal mechanical and chemical performance with time, while being of easy, quick and cost-effective fabrication.
Therefore, an object of the present invention is to provide valves that can combine excellent performances with an equally practical and cost-effective fabrication.